Thanks for the comments; I am somewhat hesitant to "rule out" certain arms, so if I don't mention some, it is becasue either I have not tried them extensively, or at all. I do not have the luxury of testing many of them from both a time and finance standpoint. What I can say is that recently, I ran into a problem with an old VPI arm that made me aware once again of how unbelieveably critical the horizontal bearing must be. This was an arm that I had rebuilt a VDH cart for, and the owner told me it sounded bad at cetain moments. I thought - well - I made some mistake in the rebuild, OR it had failed afterwards. I retested the VDH, and it was fine....I wound up testing his old VPI, and found the cup bearing in the arm had a forward to back score mark, causing a very tiny forward and back play in the arm. It was hard to feel, but it was there. When I ran a sweep, the cart DISTORTED - and I mean distorted - at a few midband frequencies. With music, it was there, but of course, much more obvious with swept sine wave. Upon replacing the bearing, all was well. I called Frank Schroder, and shared the experience of my re-affirmed faith in bearing requirements, and he laughed at me. I had forgotten JUST how critical this is. Mind you - the VPI arm is MASSIVE at the rear - so one would think that a tiny amount of play would NOT be such a huge problem. It is. I got religion all over again.
I use VPI arms becaue they let me swap arms quickly and compare carts. And I like the build quality of the tables. I use a Schroder SQ reference arm becasue it has less play than any "bearing" arm. Frank's new Artemis arms were explained to me by Frank in terms of the bearing arrangement. Genius. So, I am a fan of these - again - I have not had the opportunity to try many arms. Someone who HAS time should set up an experiment to measure horizontal energy damping in arms. I am glad to advise - but it has to be done properly - the person had be well instrumented and retired.
Now Frank has researched arm materials. The Black Palm used in his arm has complex properties - and that is why its used. Frank is very metiuculous in his selection of materials and their implementation - I beleive him to be a genius in this field of audio. This does not of course mean that there are not other great arms. This is my experience with him and his, and many discussions we have had.
Cantilever materials are complex, as are their geometries. Yes, as you describe, you DO get greater rigidity with larger diameter - but you also get more ringing and less damping. But thinning to reduce mass causes other problems, whereas the thicker, SOFTER alloy aluminums may do better. It is a matter of trial and error, and intuition; one must measure tracking, and spectral distortions to see what is happening with any material or geometry for cantilevers. In terms of styli shapes, there is so much to say I cannot cover it here. There are "faux" ellipticals, and "real" ones in terms of contact area. There are high end shibata's, and bonded cheap ones. There are varied forms of microline designs.
Waht I have found is that true ellipticals, and moreso certain line contacts (Panasonics bi-radial design was fantastic) can do VERY well in terms of stability in the groove at high frequencies. Some of the microlines have better performance in terms of inner groove hi-freq. TRACING and some aspects of reproduction due to "radiius of curvature" performance (ability to follow the hills and valleys) BUT are not as "stable" in terms of jitter - therefore CAN, under certain circumstances, have poorer channel separation, poorer linearity, and provide less samples/sec.
Samples/sec?? And you thought cartridges were analog. They are not. They take samples as they travel down the groove, bouncing and banging thier way between the walls. Like a tire on a bumpy road. What does that cause?? Groove noise. Noise, which most folks think comes from "stiction" - a rock being scraped down a plastic groove. Makes sense, but thats not the cause of groove noise.
It is the resonant frequency of the moving mass inside the cart - cantilever, coils (or armature) and suspension... etc....that makes groove noise. And what makes a cart digital. When the moving mass is excited in most MC carts, it resonates between 30-50 Khz. The problem is that even though this is above hearing, the SUM and DIFFERENCE products of this spectral noise create a wash of signals directly in the top of the audible audio spectrum, and sounds like (white) "groove noise". Lowering the moving mass RAISES these resonant frequencies, and can LOWER the amplitude of them, so that the sum and dfiff products dont make it so far down into the audio band, while at the same time reduce stylus jitter amplitude; you get less jitter, and it occurrs at a faster rate. Lower amplitude jitter?? Higher rate of jitter?? (digital samples) means more micro details exactly becasue you are taking more samples/second - you are statistically staying in better contact with the grooves walls . And making less noise. That is, in part, why I am such a believer in lowering the effective mass and precision damping - thats why I believe in and build ultra low moving mass MI and SG carts. The Soundsmith MI carts resonate between 60-80Khz, and the Strain Gauge at 120Khz with far less "stored energy" in the effective moving mass - so the amplitude of the resonance is lower. I believe that is why many folks say that our cartridges are very, very (or in the case of the Strain Gauge) extremely quiet in the groove, and why in reviews and emails folks often mention low groove noise and say - "its like I never heard my vinyl before". That is why I am a believer in going the engineering direction I have with cartridges, although it is an uphill battle, because MC carts dominate the market and are often thought of as the best engineering direction.
Bear in mind that cantilever materials become LESS of an issue when you do these things - which makes common sense - if there is less jitter amplitude, there is less damping required. The higher frequency resonances create their own set of unique damping requirements and challenges however, but are easier to deal with those with larger amplitude and lower frequency (30-50Khz). Nothing is perfect.
When I worked at Bozak, Rudy once said to me (regarding a wideband 6" aluminum cone speaker driver design I did for thje MB-80 miniature) "for any moving system, there are ten things you'd like to do - you are only going to get to do about 3 of them. You'd better choose wisely".
So think of a racing tire on a rough road. How do you get better control - more "statistical" time of the tire on the road?? You want to lower the tire/rim mass, choose the right materials, fine tune the suspension, and get the energy into the car frame. Sounds like a familar problem??? You bet.
I will likely dissappear off this blog for a while - but feel free to commnet as I might see it - long week coming up with a live recording on Sat May 14th of the Jon Pousette Dart Band for my DirectGrace record project @ Soundsmith - These recordings are to rescue children in slavery. Please take a look at
http://www.directgrace.org
Lots or work to do to set up for this recording - we will have a live audience of invited folks at the Soundsmith....we are full up yet with audience at this time, as Jon and I wanted not only "live" sound for the record, but an appreciative audience a-hootin and a-hollerin - and those who will hear his band will be so moved. I hope the recording is good enough for the DirectGrace project. We are hoping to record another Bill Frisell record this summer - Bill said that he may have the time. These are artists who have been VERY generous with their talent and time for the sake of these children. If you want to know more about why I am doing this - please look at the trailer on the website for the movie -
http://www.stolenchildhoods.org
The DirectGrace project is a 501C3, not for profit effort, and contributions are accepted through the John Herrick Jackson foundation. If you feel so moved, please contact me. We accept all comers with any form of help.
Many thanks -
Peter Ledermann/Soundsmith
